Bias Optimized IP2 & IP3 Linearity and NF of a Decade-Bandwidth GaN MMIC Feedback Amplifier Kevin W. Kobayashi Motivation • Future GaN trends – Power Density Wideband Linearity – Higher frequency – Lower voltage • GaN Linear Front-end Applications – Software Defined Radios (SDR) – Next Gen BTS – CATV /Fiber (FTTX) • Common Need: > Octave-BW, higher linearity, LNAs, PAs • New Challenge: High IP2, IP3, and low noise simultaneously • This work – Investigates the optimum NF, IP2, IP3 bias of a GaN Cascode Amplifier State-of-the-Art GaN MMIC Noise Figure 4 Noise Figure (dB) 3.5 [CSIC 2011] [14] 8W 3 [11] 0.4W [1] [14] 4W 2.5 6.5W 2 [3] ~1W [4] 0.3W 3.3W [9] 1.5 1 Wide-band flat-gain LNAs [2] 0.15W [10] [5] 0.3W 1.2W [6] 2-Watt Best NF, Poor gain roll-off 0.5 [7] 2-W(T= -10C) [RFIC 2012] 0 0 1 2 3 4 5 6 7 Frequency (GHz) This work reveals new bias optimized NF & power capability of a 250M-2GHz decade-BW flat-gain LNA 8 Cascode vs. Common-Source DC I-V Comparison A/mm 1.2 IDS (A/mm) 1.0 COMMON-SOURCE CASCODE Vdd 0.8 + Vds2 - 0.6 + - Vds1 0.4 50 Ohm Load Lines 0.2 0.0 0 10 20 30 40 50 60 70 80 VDS Cascode provides flatter output conductance and sharper knee voltage than a common-source better for linearity Cascode I-V : Various Vdd Operation more linear 1.2 Vds1 = 10V Vds1 = 15V Vds1 = 20V Vdd = 20V Vdd = 30V Vdd = 40V Ids A/mm) 1.0 Vdd + Vds2 - 0.8 0.6 Vg2 + Vds1 - 0.4 50 ohm 0.2 0.0 0 10 20 30 40 50 60 70 80 Vdd (V) Constraining Tj1=Tj2 means adjusting Vg2 so Vds1=Vds2. wider linear voltage swing is achieved at higher Vdd. Cascode vs. Common-Source MAG Comparison Wg = 500um HEMT Max Gain (dB) 50 40 CASCODE 30 20 10 COMMON-SOURCE 0 0 10 20 30 40 50 60 70 80 90 100 Frequency (GHz) Cascode provides over 10 dB greater maximum available gain due to reduced Miller capacitance and higher output impedance. GaN Cascode Feedback Design + Vds2 - + Vds1 - GaN Cascode Feedback LNA • Cascode -Thermal -Electrical • Wg_total = 2 mm • Vdd = 10-40V • Idd = 200-500 mA 4 finger x 125um (Wg=500um unit cell) Chip size is 1.6x1.3 mm2 Noise Figure Bias dependence NF @ 2 GHz Noise Figure (dB) 2.5 2.0 40V 1.5 30V 25V 1.0 20V 10V 0.5 0.0 50 100 150 200 250 300 Idd (mA/mm) Noise Figure is strongly voltage dependent. Current dependence is stronger at higher voltages. IP3 Bias dependence IP3 @ 2 GHz 60 IP3 (dBm) 55 40V 50 30V 45 25V 40 20V 10V 35 30 50 100 150 200 Idd (mA/mm) 250 300 IP3 is strongly voltage dependent. At higher Vdd, a larger linear swing is enabled w.r.t. the Cascode knee voltage. IP2 Bias Dependence IP2 @ 2 GHz 80 IP2 (dBm) 70 40V 30V 60 25V 50 20V 40 10V 30 50 100 150 200 250 300 Idd (mA/mm) IP2 increases with high voltage. Unlike IP3, IP2 has an optimum efficient bias (25V-150mA/mm). Wide-band S-parameters Performance Gain & Return-Loss (dB) 40V-500mA 30 S21 20 3-dB BW ~ 3.5 GHz 10 0 S11 -10 -20 -30 S22 -40 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Frequency (GHz) Cascode FB design achieves flat-gain decade-BW response Noise Figure at Select Biases 40V-500mA- High Linearity Bias 2.83 Noise Figure (dB) 3.0 2.5 10V-200mA - Low NF Bias 2.28 2.08 2.20 2.57 2.53 1.42 1.42 1.32 1.32 3.0 3.5 2.19 2.0 1.48 1.5 1.23 1.09 1.10 1.24 1.0 1.01 0.5 0.0 0.5 1.0 1.22 1.08 0.89 0.88 1.5 2.0 2.5 Freuency (GHz) Low NF bias: sub-1 dB NF and > 1-Watt P1dB High DR bias: sub-1.5 dB NF and > 3-Watt P1dB IP2 Performance 80 68.4 70 60.7 IP2 (dBm) 60 66.1 58.1 67.2 58.9 70.5 59.6 72.2 75.6 67.1 60.0 64.5 64.1 50 40 30 40V-500mA High Linearity Bias 20 25V-300mA Good Dynamic Range Bias 10 10V-200mA Low Noise Bias 0 0 0.5 1 1.5 2 2.5 Frequency (GHz) 3 3.5 Excellent broadband IP2 as high as 70 dBm is achieved from single-ended design w/o the use of a balanced topology! IP3 Performance 60 52.5 50.3 49.3 50.6 50.9 49.2 49.6 48.3 47.5 46.5 46.1 46.1 44.6 44.0 IP3 (dBm) 50 40 30 40V-500mA High Linearity Bias 20 25V-300mA Good Dynamic Range Bias 10 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Frequency (GHz) IP3 > 50 dBm is achieved at high bias. Good IP3 > 46 dBm is achieved at moderate bias where NF < 1.5dB (Good DR) P-1dB & P-3dB (dBm) P1dB & P3dB Performance 45 40 35 30 25 20 15 10 5 0 39.0 30.9 38.7 31.1 38.0 38.1 37.7 36.6 35.6 30.9 30.9 30.8 30.3 29.6 40V-500mA - P1dB High Linearity Bias 40V-500mA - P3dB High Linearity Bias 10V-200mA - P1dB Low Noise Bias 0.0 0.5 1.0 1.5 2.0 2.5 Frequency (GHz) 3.0 3.5 Pout capability ranges from 1W to 8-W with a corresponding NF range from sub-1dB to 3 dB. IP3-NF: Technology Comparison Summary of S-band LNA & Gain Block Performance 55 [This Work] [14] 50 HBT-WB HBT-NB [14] OIP3 (d Bm) GaN [6] 45 HFET [12-13] [3] [7] 40 D PHEMT E PHEMT [10] E-PHEMT 35 [1] GaAs HBT HFET/MESFE T GaN HEMT [5] 30 NB= Narrow band tuned WB= Wide band tuned D-PHEMT 25 0 1 2 3 4 5 6 7 Noise Figure (dB) GaN achieves best combination of OIP3 and NF over other technologies. Cascode FB enables decade BW operation. 8 Summary • Benchmarked decade-BW flat-gain – Flat 20 dB gain – NF as low as 0.88 dB with P1dB > 1-W – Best IP2-IP3-NF combination • Good linearity FOMs – (for decade BW) – IP3/Pdc LFOM ~ 5.2:1 – (IP3-P1dB) ~13.4 dB – Improve with GaN device maturity • Future work – E-mode GaN (self-bias) – MISFET (lower gate noise) – Base-band to mmW